OBJECTIVE: The aim of this study was to determine the etiology and natural history of acute superior mesenteric venous thrombosis (MVT) with and without splenic or portal vein involvement. METHODS: A retrospective analysis was carried out of patients with acute superior MVT evaluated between 1979 and 1998. Case records were reviewed and a questionnaire mailed to patients for follow-up evaluation. Also, a search was made to identify etiologies such as malignancy, infection, inflammatory bowel disease, and other risk factors. Patients were divided into two groups, isolated MVT or MVT with splenic or portal vein involvement. RESULTS: A specific etiology (malignancy, thrombophilia, inflammatory bowel disease, or surgery) was found in 35 of 69 patients. Thirty patients had isolated MVT with involvement predominantly of the small mesenteric veins; in the remaining 39 there was also portal or splenic vein involvement. Patients with isolated MVT were less likely to be diagnosed by imaging studies such as ultrasonography and CT and more likely to have bowel necrosis, and they required surgery more frequently. Inherited hypercoagulable disorders were more often found in patients. with isolated MVT. During follow-up, six patients had recurrent MVT, and one patient with combined mesenteric and portal vein thrombosis developed variceal bleeding. CONCLUSIONS: Patients with isolated MVT are more likely to have hypercoagulable disorders. Isolated MVT is more difficult to diagnose and more likely to require surgery. Classification of patients with MVT into those with small vessel involvement or those with splenic or portal vein involvement thus has important clinical and prognostic value. Patients surviving the initial period have a good prognosis but definite risk of recurrence. Risk of variceal complications appears low.
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